1. Field of the Invention
The preferred embodiments of the present invention relate, inter alia, to a continuously variable transmission control device, a continuously variable transmission, and a vehicle equipped with the same.
2. Description of the Related Art
The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
In known art, an electronically controlled continuously variable transmission (hereinafter referred to as “ECVT”) capable of continuously varying the transmission gear change ratio or the transmission ratio (hereinafter referred to as “transmission ratio”) is used in vehicles, such as, e.g., scooter type motorcycles, or so-called four wheel buggies.
Normally, an ECVT includes a primary sheave that rotates together with an input shaft, a secondary sheave that rotates together with an output shaft, a belt wound around both the primary sheave and the secondary sheave, and an actuator for varying the belt groove width of the primary sheave. Furthermore, the above-mentioned vehicle includes a control device for controlling the ECVT actuator. The control device controls the actuator and changes the transmission ratio based on a driving state of the vehicle, such as, e.g., a vehicle speed, an engine speed, or a throttle opening degree, and also based on a transmission ratio map which shows the relationship with the transmission ratio. Accordingly, in vehicles equipped with an ECVT (hereinafter referred to as “ECVT-equipped vehicle”), it is not necessary for a rider to perform the gear shift operation and/or the clutch operation.
Specifically, the primary sheave normally has a movable sheave provided on the input shaft in an axially slidable manner and a fixed sheave fixed on the input shaft in an axially immovable manner. The actuator is connected to the movable sheave of the primary sheave. The movable sheave of the primary sheave is driven by the actuator and slides in the axial direction of the input shaft. This varies the width of the belt groove of the primary sheave.
Furthermore, the secondary sheave has a movable sheave provided on the output shaft in an axially slidable manner and a fixed sheave fixed on the output shaft in an axially immovable manner. A spring for urging the movable sheave toward the fixed sheave side is connected to the movable sheave of the secondary sheave. The movable sheave of the secondary sheave is constantly urged toward the fixed sheave side by the spring. For this reason, a load in the direction that narrows the width of the belt groove (in the direction that widens a winding radius of the belt) is constantly applied to the secondary sheave. Thus, the primary sheave constantly receives a load in the direction that widens the belt groove width (in the direction that narrows the winding radius of the belt) from the secondary sheave side.
With this kind of structure, when the movable sheave of the primary sheave slides toward the fixed sheave, the belt groove width of the primary sheave is narrowed, and the winding radius of the belt is enlarged. Accompanying this action, the belt in the secondary sheave belt groove is moved radially inward toward the secondary sheave, and the movable sheave of the secondary sheave moves in the direction away from the fixed sheave against the urging force of the spring. In this way, the transmission ratio becomes smaller, and the movable sheave moves closer to the so-called Top position at which the transmission ratio is at a minimum.
On the other hand, when the movable sheave of the primary sheave slides in the direction away from the fixed sheave, the belt groove width of the primary sheave widens, resulting in a reduced winding radius of the belt. Accompanying this action, the belt in the secondary sheave belt groove is moved radially outward toward the secondary sheave, and the movable sheave of the secondary sheave moves toward the fixed sheave by the urging force of the spring. In this way, the transmission ratio becomes larger, and the movable sheave moves closer to the so-called Low position at which the transmission ratio is at a maximum.
Meanwhile, normally the control device controls the actuator such that the movable sheave of the primary sheave returns to the Low position at which the belt groove width is at its widest and the transmission ratio is at the maximum when the vehicle is stopped (including idling). Moreover, the control device controls the actuator so that the movable sheave of the primary sheave returns to the Low position when the power is turned on.
However, for example, when the power is turned off just after driving is stopped through sudden braking, the actuator sometimes stops without having fully returned the primary sheave to the Low position. Moreover, if the power is turned on again in this state, only the movable sheave of the primary sheave will move by itself to the low position in a state in which the belt is not rotating. In other words, despite the belt not rotating, the belt groove width on the primary sheave side widens. Thus, the belt may come off from the primary sheave.
However, if the belt comes off from the primary sheave, the primary sheave will idly rotate without the belt such that no force will be transmitted to the belt. Furthermore, if a sheave position control for sliding the movable sheave of the primary sheave in order to vary the transmission ratio starts in this state, the belt to which force is not being transmitted due to the belt having come off from the primary sheave will be sandwiched by the primary sheave whose rotation speed has been increased to some degree. This will cause sudden transmission of the force to the belt. This action causes unsmooth acceleration, resulting in poor riding comfort.
Therefore, it has been proposed that, when the groove width of the primary sheave at the time of starting the engine is narrower than a stipulated groove width set in advance, a transmission ratio control (in other words, sheave position control) is not performed up to the point when the engine speed has exceeded a stipulated speed change permissible speed and the transmission ratio control is initiated after the engine speed has exceeded the speed change permissible speed (see, for example, Japanese Patent No. 3375362 (hereinafter referred to as “Patent Document 1”)
With the ECVT control device described in Patent Document 1, it is presumed that the belt will rotate together with the primary sheave when the engine speed exceeds the speed change permissible speed. In reality, however, it cannot be determined certainly whether the primary sheave is idly rotating with the belt. In other words, if the primary sheave is rotating together with the belt, it can be determined with certainty from the engine speed that the belt is rotating. However, if the primary sheave is idly rotating without the belt, rotation of the belt cannot be confirmed by the engine speed. For this reason, with the above-described control device, even if the primary sheave is idly rotating without the belt, the sheave position control may inadvertently start because the engine speed has exceeded the speed change permissible speed. Accordingly, with the ECVT control device described in Patent Document 1, whether the primary sheave is rotating together with the belt cannot be detected with certainty. As a result, it may be difficult to solve the issue of being unable to achieve smooth acceleration when the primary sheave is idly rotating without the belt.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. For example, certain features of the preferred embodiments of the invention may be capable of overcoming certain disadvantages and/or providing certain advantages, such as, e.g., disadvantages and/or advantages discussed herein, while retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.